Distributed Combustion: A Mechanism of Acoustic Suppression,
BRIGHAM YOUNG UNIV PROVO UT
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Acoustic suppressants apparently work by one of three mechanisms energy loss due to viscous dissipation of drag forces, modification of the propellant combustion response function, or energy interchange due to distributed combustion. Viscous dissipation of acoustic energy by drag forces on a suspended particle is the most commonly recognized mechanism, being a direct analogy to suspended moisture in fog. A second mechanism whereby an additive can effect acoustics occurs at the burning boundary of the system. Solid additives within the propellant can have a catalytic influence on the propellant combustion, modifying the combustion response. The best known example of this is probably Al2O3. Al2O3 is the particulate product of aluminum combustion which provides the viscous drag dissipation previously discussed. However, Al2O3 is also a weak combustion catalyst in composite propellants. An additive that influences the steady burning of a propellant can also be expected to influence the transient response of the propellant. The third mechanism considered is due to the effect of a particle burning as it traverses a relatively large portion of the system. As it does so, the interchange of energy between the burning particle and the acoustic environment can result in either a driving or damping contribution to the acoustics of the system.